linux-kernel - Re: iwlwifi: Regression after migrating to 6.6.32

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Date: Thu, 13 Jun 2024 12:36:59 +0200
From: Johannes Berg <johannes@...solutions.net>
To: Baochen Qiang <quic_bqiang@...cinc.com>, Fabio Estevam
 <festevam@...il.com>
Cc: miriam.rachel.korenblit@...el.com, kvalo@...nel.org, Jakub Kicinski
	 <kuba@...nel.org>, linux-wireless <linux-wireless@...r.kernel.org>, 
 linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: iwlwifi: Regression after migrating to 6.6.32

On Thu, 2024-06-13 at 17:51 +0800, Baochen Qiang wrote:
> > 
> > Not sure that means anything though, I really would have expected a 4k
> > buffer to be 4k aligned - why would you even want to map it across two
> > pages?
> IMO SWIOTLB manages buffers in a unit of IO_TLB_SIZE, it does not care about whether or not we are crossing page boundaries, no?

Well arguably it should have some 'natural' alignment guarantees?

> > 
> > If it is SWIOTLB, shouldn't we get into this condition?
> > 
> >         /*
> >          * Historically, swiotlb allocations >= PAGE_SIZE were guaranteed to be
> >          * page-aligned in the absence of any other alignment requirements.
> >          * 'alloc_align_mask' was later introduced to specify the alignment
> >          * explicitly, however this is passed as zero for streaming mappings
> >          * and so we preserve the old behaviour there in case any drivers are
> >          * relying on it.
> >          */
> >         if (!alloc_align_mask && !iotlb_align_mask && alloc_size >= PAGE_SIZE)
> >                 alloc_align_mask = PAGE_SIZE - 1;
> > 
> This is not present in 6.6.32 stable kernel.
> 

Oh. So I guess try to pick up commit 14cebf689a78 ("swiotlb: Reinstate
page-alignment for mappings >= PAGE_SIZE").

johannes